merging in PR #52 - #57
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Adds screen-space motion vectors (per-pixel Δpixels between the current
and previous frame's projected position of the same world point). This
is the essential input for temporal upsamplers like DLSS, FSR2, and
XeSS. Without it, applications must approximate motion vectors from a
full-screen camera-only depth reprojection, which cannot represent
per-object motion and causes visible ghosting on moving geometry.
New public API:
* BN_FB_MOTION channel enum (vec2f per pixel, screen-space pixel delta)
* bnSetInstanceMotionDeltas(model, slot, BNTransform*, n) - per-instance
motion delta transform, defined as prev * inverse(curr). Optional;
when unset, only camera motion contributes.
* ANARI parameters on Camera: motion.viewProjection and
motion.previousViewProjection (both ANARI_FLOAT32_MAT4). Both must
be supplied for the motion channel to be written.
* ANARI parameter on Instance: motion.transform (ANARI_FLOAT32_MAT4,
the instance's transform on the previous frame). Optional per
instance; defaults to the current transform.
* ANARI framebuffer channel: channel.motion (ANARI_FLOAT32_VEC2).
Design choices:
* Delta form (prev * inv(curr)) rather than raw prev transform,
computed on the ANARI shim side. Barney has no device-side
per-instance current-transform array (transforms live inside the
RTC/OptiX BVH), so shading with raw prev transforms would require
inverting the current transform per pixel in the hot ray shader
path. Delta form is one CPU inverse per instance per frame in
exchange for zero inverses in the kernel.
* Screen-space pixels rather than world-space velocity: matches
DLSS/FSR2/XeSS conventions and DirectX/Vulkan raster MV output.
Zero downstream reprojection needed.
* BN_FB_MOTION added to FrameBuffer::needHitIDs() mask - the shade
kernel reads hitIDs[tid].instID to look up per-instance motion
deltas, and without this the hitIDs buffer is never populated for
motion-only channel requests.
Shading:
In shadeRays.cu, at the accumID==0 && generation==0 aux-write block:
world_hit = ray.P
prev_world = motionDeltas[instID] * world_hit (if deltas supplied)
delta_ndc = 0.5 * (project(curr_vp, world_hit) -
project(prev_vp, prev_world))
motion = delta_ndc * fbSize (in pixels)
Guarded by camera.haveMotionMatrices - falls back to no-op if the app
did not supply the motion.viewProjection matrices.
Framebuffer plumbing:
* MotionChannelTile (vec2f per pixel) parallel to AuxChannelTile
* TiledFB: alloc + linearize kernel (linearizeMotionTiles)
* FrameBuffer: linearMotionChannel staging + gatherMotionChannel +
writeMotionChannel virtuals; MPI-gather runs in finalizeFrame() so
send/recv pair correctly across all ranks
* DistFB: MPI send/recv path templated on MotionChannelTile
* LocalFB: single-node overrides
resetAccumulation() extended to zero the motion tiles on every device
at the start of each frame - the shade kernel writes only on hits, so
unwritten pixels (background) would otherwise retain stale motion
values from previous frames, causing 'ghost silhouette' artifacts.
Backward compatibility: all changes are additive. Existing apps that
don't request BN_FB_MOTION are unaffected. Existing sample apps
verified to produce identical output.
Testing: full end-to-end verified on three ANARI examples with correct
motion vectors driving NVIDIA DLSS temporal upscaling. Motion vector
corruption tests (zero / negate / exaggerate / noise) confirm DLSS
consumes the channel and its output measurably degrades on corruption.
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This merges in @mvictoras PR #52 , with all conflicts resolved via this MR